Sounds include audible and inaudible sound waves. Frequency ranges of sounds that are audible to humans vary based on the individual but commonly are said to include a range of 20 to 20,000 hertz (Hz). Different species have varying abilities to hear sounds of different frequency ranges, and many animals are capable of hearing and detecting sounds that most people cannot hear or feel. For example, the ability to detect sound vibrations and sounds below the range in which humans can hear is common in elephants, whales, and other animals. Unlike people, animals may be alerted to danger when sound vibrations are detected that are inaudible to humans. However, humans may be susceptible to danger when inaudible frequencies are occurring because they may not be aware that such sounds are occurring.
For example, low frequency sound exposure for even short periods of time can cause damage to humans, such as temporary or permanent hearing loss and other physical changes (e.g., confusion, mood changes, and headaches, among others). Oftentimes, the low frequency harmful sounds are inaudible or undetectable to the people being harmed by them.
Another problem is the fact that people can lose their range of hearing due to various factors, including age, injury, infection, and exposure to toxins. In addition, people may be born with a limited or missing ability to hear. Thus, sounds can occur without people's awareness regardless of whether they are at a harmful frequency or not. In addition, there can be security concerns associated with sounds, including inaudible sounds. For example, electronic applications can use inaudible or undetectable sounds to gain information (e.g., by bypassing security systems to gain access to personal data) so that a targeted user could be completely unaware that data is being collected without their consent. Also, as discussed above, sounds (such as low frequency sound exposure) can be used as a weapon.